Onana is definitely not a good choice, he does not give even a fraction of the confidence that David de Gea gives. It would be good to release him immediately for Amorim, in fact he has a lot to think about, it is quite difficult to make this team proper for the next season. Many managers could not do it, Amorim may share this fate, maybe next season, it would not be right to comment on this season, we will see what he will do next season.
I don't think if Manchester United has plans regarding Onana next season, what if they even sold him to sign a goalkeeper whom they will spend less but give quality keeping because the amount they spent on him is very high, so actually as Manchester United is badly in need of money they shouldn't have or keep someone that's receiving high but given less to the club and truly Onana is given less to Manchester United, perhaps Amorim has not thought about his situation yet which means there will be next season for Onana and Manchester goal post will remain unstable as always.